oni no karada 鬼の体 body features of an Oni Demon
oni no shintai 鬼の身体 - oni no sugata 鬼の姿
Oni are born out of the imagination of human beings - they have the physical characteristics of things humans fear, mostly in animals.
Their appearance changed during the long history of Japan, from the Heian period to our present popular Setsubun-Oni.

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Depictions of oni vary widely but usually portray them as hideous, gigantic ogre-like creatures with sharp claws, wild hair, and two long horns growing from their heads. They are humanoid for the most part, but occasionally, they are shown with unnatural features such as odd numbers of eyes or extra fingers and toes. Their skin may be any number of colors, but red and blue are particularly common.- - - More in the WIKIPEDIA !

Emori えもり瀬兵衛 （せへえ） Emori Seei
Emori was able to buy something special. He got a tooth from a person living in 八丈島 Hachiojima, where the original inhabitants were said to be Oni.
The tooth was about 3 cm long and 6 cm wide.

When a child looses an upper tooth, it has to throw it under the veranda and chant
nezumi no ha to tokkaero 鼠の歯ととっかえろ Change this into the tooth of a mouse.
When it looses a lower tooth, it has to throw in on the roof and chant
oni no ha to tokkaero 鬼の歯ととっかえろ Change this into the tooth of an Oni.
Thus the new tooth will grow strong and healthy.

Sutten Doji 酒顛童子 / スッテンドウジ Shuten Doji
Shuten Doji was beheaded by Minamoto Yorimitsu and his head flew up into the sky. Then it came down and landed on the helmet of Yorimitsu. With his strong teeth of an Oni it started to bite off the layers of the helmet and almost succeeded, leaving just one layer before it was chased away.

When Sakanoue no Tamuramaro drove out the demon of this region, the teeth of this Oni were left over.
The boss of the native 蝦夷 Emishi group was called 赤頭 Akagashira. - alias Aterui アテルイ / 悪路王 Akuro-O / Acro-O 阿弖流爲 (? - 802)

赤頭 Head of Akagashira

and his oni no kiba 鬼の牙 demon teeth

Tamuramaro built a grave for Akagashira and offered a statue of Kannon Bosatsu to appease his soul. This is now at the temple 竜福山・長谷寺 Hasedera.
When they dug out the grave in 1704, they found 33 teeth in the skull of this Akagashira Oni.
ケセンの鬼の国 Kesen is the land of the Oni.

The local Oni heard to Buddhist lectures of Saint Honen, abdicated his bad ways, wrote a Buddhist name on his horns and threw his body down a cliff.
To appease his soul, the temple 鬼骨寺 Kikotsu-Ji "Temple of Demon Bones" was built.
The temple 法泉寺 Hosen-Ji venerates his myoogo 名号 Myogo, Buddhist name, the horns 鬼角.
The temple 西福寺 Saijuku-Ji venerates 鬼の歯 his teeth.